In January 1998, NASA astronaut Andrew Thomas boarded Space Shuttle Endeavor for his second-ever space flight. It would be more than four months before he returned to Earth. Endeavor traveled outside of Earth's atmosphere, docked with the Russian Space Station Mir, and exchanged Andy Thomas with U.S. astronaut Dave Wolf, who had lived aboard Mir since September 1997.

On March 23, 1998, with about half of his stay aboard Mir behind him, Andy Thomas met Scientific American Frontiers host Alan Alda for a live interview.

U.S. presence on Mir is yielding important information about how humans can survive and thrive in space for long durations. That knowledge is helping to build a foundation for a human mission to Mars, which NASA is considering for sometime around the second decade of the next century. It may take as long as 26 months to travel from Earth to Mars. In that time, astronauts will be too far away to look back and see Earth -- how will they be affected by the distance and the darkness between themselves and their home?

Scientific American Frontiers producers are planning a one-hour special devoted to Mars for their 1998-99 season. The PBS special will examine the logistics of a human mission to Mars and the preparations that are underway. Alan Alda's interview with astronaut Andy Thomas is one important step in making the Mars special a reality.

The live interview gave viewers an opportunity to hear Andy Thomas's thoughts on a human trip to Mars. Alan Alda asked Andy Thomas about his experiences aboard Mir and what it's like to be so far from home. They talked about the physical and psychological effects of living in space, and about methods for counteracting those effects, including exercise programs and computer-programmed "surprises" designed to help astronauts feel connected to their friends and families.

The interview was preceded by a 15-minute set-up period, featuring Alan Alda and producers getting ready for their talk with Andy Thomas. This groundbreaking event was made available by PBS Online with assistance from RealNetworks.

Scientific American Frontiers is wholly underwritten by GTE Corporation, now Verizon Communications Inc. Frontiers airs on PBS with five new programs each season.

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Space Station Mir was launched into Earth's orbit from Russia in 1986. Russian scientists devised a plan that called for the launch of the main section of Mir first, and then later sending additional modules that would dock with Mir and become a part of the space station. According to the plan, Mir's final configuration would allow it to house six people, three of whom would rotate every two to four months. The station was designed to operate for at least 10 years.

The name Mir has a few different translations. The official translation is "peace," but Mir can also be translated as "commune" or "village." On a somewhat smaller scale, it has become a commune or village. Today Mir can be permanently staffed by two or three cosmonauts. Visiting crews have raised Mir's population to six for up to a month at a time.

Above all, Mir is a home for scientific research, the likes of which cannot be done on Earth. When Mir was launched, its research goals were focused in six main areas: space technology, astrophysics, resources, technology, biotechnology, medicine and biology. Mir provides an opportunity to conduct experiments in microgravity for a much longer amount of time than has ever been done before. Humans who inhabit Mir are not just the conductors of experiments -- they are the subjects of study into the effect of long stays in space on the human body and mind. Our work on Mir is designed to propel us forward into the future of space exploration -- which is now just around the corner.

Since 1995, NASA has been sending astronauts to live on the Russian space station Mir. In all, seven astronauts have been residents of Mir -- Andy Thomas is the last. His return to Earth marks the completion of what is commonly known as International Space Station Phase I, a NASA program designed to learn more about the cooperation of people from different countries living together in space and about the day-to-day operating procedures needed to maintain a space station.

The next several years will bring exciting new developments in space exploration. Aside from the possibility of sending a human mission to Mars around 2012, plans are underway for the International Space Station, which will be built with the cooperation of 15 countries. The first components of the International Space Station are scheduled to launch into orbit as early as May 1998. The experience gained through living on Mir provides a unique opportunity to prepare for some of the challenges the International Space Station will present.

The ability to conduct long-term scientific research in space is important to the future of the U.S. space program. Plans for an International Space Station and a human mission to Mars will both require humans to spend an extended amount of time in space, and we need to gather as much advance information about long-term space stays as possible. But the average space shuttle flight lasts no longer than several days or at most a few weeks. That amount of time isn't long enough for scientists to complete some of their investigations.

That's why NASA's work with Mir is so important. The NASA-Mir program is a unique opportunity for U.S. and Russian scientists to work together for mutual gain. With preparations underway for the International Space Station, life on Mir is a chance for a dress rehearsal of sorts. Experiences aboard Mir will help hammer out some of the logistics of designing, building, staffing and operating a multi-national space station.

How does NASA benefit from Mir? Aside from learning about the effects of long-duration space travel on the human body, scientists have conducted other experiments into how to support extended space travel, including growing wheat aboard Mir in a long-term program that called for cooperation from both American astronauts and Russian cosmonauts. NASA has also tested space docking techniques and examined the shuttle's ability to redirect the attitude of an orbiting object (its orientation toward the sun).

What does the Russian space program get in return? NASA space shuttles will dock with Mir nine times during this phase of the NASA-Mir program. When the shuttles rendezvous with Mir, they bring supplies, station maintenance equipment and science experiments, as well as an American crew member who will live aboard Mir. Samples taken aboard Mir can also be returned to Earth on the shuttle, which provides plenty of refrigerator and freezer space.

A NASA astronaut first went to live on Mir in March 1995. Andy Thomas, the seventh and last U.S. astronaut to live on Mir, is currently on board and will return to Earth in May 1998. NASA's program to send astronauts to Mir, known as International Space Station Phase 1, serves as a foundation for building the International Space Station in Phases 2 and 3, set to begin in 1998.

The knowledge we gain from working on Mir will also be useful as NASA prepares for an occupied voyage to Mars, probably in the second decade of the next century. It may take as long as 26 months to travel from Earth to Mars. Before the trip is made, scientists need to know as much as they can about how the human body is affected by spending a long period of time in space, as well as how plants and animals function in microgravity over a long period of time. Mir provides the perfect opportunity.

In this interview, Scientific American Frontiers host Alan Alda talks with Andrew S.W. Thomas, Ph.D., the NASA astronaut currently living on Russia's Mir Space Station. Dr. Thomas plans a four-month stay on Mir -- he left Earth on January 22, 1998, on the Space Shuttle Endeavor and arrived at Mir on January 25. His return flight to Earth is scheduled for May 29, 1998. Dr. Thomas is the seventh and last U.S. astronaut scheduled to live aboard Mir as part of Phase 1 of the International Space Station program.

Dr. Thomas, a native of South Australia, reported to NASA's Johnson Space Center in Houston, Texas, in August 1992. He qualified to be a mission specialist on space shuttle flight crews. While he waited for a flight assignment, his work included supporting shuttle launch and landing operations and providing technical support to several projects. Dr. Thomas's first space flight was on Shuttle Endeavor in May 1996. He traveled 4.1 million miles and completed 160 orbits of Earth during the 10-day mission.

Life on Mir could bring about a new definition of homesickness. Although Mir residents can communicate with their friends and families via ham radio and e-mail, scientists back on Earth were concerned that they may lose a feeling of connectedness with their "normal" lives. So NASA devised a system of "surprises" -- computerized messages that are pre-programmed for delivery at specified intervals throughout an astronaut's stay on Mir. Messages are recorded with astronauts' friends and families and then stored in a computer. They remain in computer storage until a pre-programmed date and are then opened for the astronaut to view.

Before astronaut Andy Thomas left Earth for Mir, Alan Alda recorded a surprise greeting for him. Andy was scheduled to receive Alan's greeting before this interview took place. During the interview, Alan will ask Andy about the surprises and how they're helping him feel connected to his "normal" life on Earth.

Mars has long been a favorite of scientists and science fiction writers alike. The Red Planet, our next-door neighbor in space, has attracted attention for a number of reasons. Mars is surprisingly similar to Earth, and is considered the most likely to have hosted extra-terrestrial life of all the planets in our solar system. Today Mars's atmosphere is largely made up of carbon dioxide, and its surface is cold and desert-like. But geologic evidence suggests that liquid water was present on Mars at one time. If that's true, what happened to change conditions on Mars to what they are today? That is just one of the questions that draw scientists to want to learn more.

In August 1996, a group of scientists announced that they had found organic compounds -- evidence of life -- in a Martian meteorite. However, other scientists have contradicted these findings. The debate has served to fuel interest in launching a human mission to Mars to collect further information and bring back samples for analysis. NASA scientists are considering a human mission, possibly as early as the year 2012. But the journey would be a long one, unlike any human space mission ever undertaken. The trip to Mars could take as long as 26 months. Our current space vessels could not carry enough fuel to complete the entire trip, so scientists must devise a way to manufacture fuel for the return trip. Food would also need to be grown or manufactured during the journey.

But the greatest unknown is the human factor. Astronauts making the trip to Mars could not look back and see the Earth. How would they deal with the psychological effects of the long, dark journey? Physical changes could play a role too -- exercise is less effective in space than on Earth, because the force exerted by gravity is reduced. Exercising on a treadmill in space, for example, produces a force of only 50 to 70 percent of one's Earth bodyweight. Finding effective ways to exercise is important to maintaining muscular strength and bone density during long stays in microgravity.

Scientific study on Mir is providing a unique way to examine the physical and psychological effects of a long stay in space. Because a human can stay aboard Mir for months, instead of just days or weeks, as in a typical space shuttle flight, scientists have a new look at preparations they'll need to make to help humans survive and thrive on a trip to Mars. Knowledge we've gained through human presence on Mir -- from improved exercise techniques to computer-programmed "surprises," from analyses of crystal growth to the cultivation of a wheat crop -- is helping build the foundation for a trip to Mars.